This invention relates to the field of vibration control, and particularly to an active inertial force generator capable of developing periodic forces of controllable frequency, amplitude, direction and phase, for cancelling undesirable vibrations developed by aircraft engines or the like.
For controlling the generation or transmission of vibrations developed by machinery, various schemes and mechanisms are well known. These fall generally into categories of (1) passive vibration dampers, such as flywheel dampers, (2) vibration isolators, such as shock mounts, (3) hydraulic vibrators for generating periodic forces to counteract undesirable vibrations, and (4) mechanical active vibration compensators. The present invention is in the last group. Within that group, there are prior disclosures of devices which are either reciprocating or rotary. U.S Pat. No. 3,208,292, for example, discloses a variable force oscillator comprising four imbalanced flywheels arranged in counter-rotating pairs on two parallel axes; a differential gear arrangement permits one to change the angle between the eccentrically weighted portions, and thus change the magnitude of the vibration developed. U.S. Pat. Nos. 3,209,525, 4,289,042 and 4,667,532 show arrangements with two or three eccentric weights. With none of these devices, however, can one simultaneously control the frequency, magnitude and direction of the generated forces, or correct the phase between another source of vibration and the device. U.S. Pat. No. 4,688,355 does show an automatic balancer of the hydraulic type for grinding machines, but it requires a stationary fixture for hydraulic pressure to act against, and is not capable of developing an inertial force for compensating or cancelling vibrations developed by another device.
None of the prior devices is capable of simultaneously altering the magnitude, frequency, phase, and direction of its vibrational forces while in operation. In short, the problem of producing compensating periodic forces of readily changeable frequency, magnitude, direction and phase is a problem only partially addressed by the prior art, and was never heretofore solved.
In view of the foregoing, it is an object of this invention to generate periodic inertial forces for cancelling engine vibrations and the like, which may have varying frequency, magnitude and direction.
Another object is to provide a system for maintaining proper phase between the cancelling forces and the undesired vibration.
A further object is to provide a rotary mechanical vibration canceller with plural rotors nested in a common plane, so as to produce force vectors only in that plane.
Yet another object is to control a vibration cancelling device automatically in response to sensed vibrations in the environment of the device, so as to match the inertial forces of the device to those of the environment.